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Abstract Bachelor Project FBT 2020-2021: Comparative study of immunochromatographic and mass spectrometric method in the detection and confirmation of Legionella colonies

BACKGROUND: The family of the Legionellaceae consists of a single genus, the genus Legionella. Within the genus there are 19 species who can cause a particular form of pneumonia called legionellosis. A distinction is made between Legionella pneumophila (L.pneumophila) and Legionella non-pneumophila species (L.non-pneumophila). In 90 % of the cases, legionellosis is caused by an infection with L.pneumophila. Thus, of all species that can cause disease, this is the most frequent pathogen. Legionella bacteria are very commonly found in different types of water systems of both natural and artificial origin. An infection with Legionella species can occur by inhaling aerosols containing these bacteria. The various types of sickness that can be seen in legionellosis are Legionnaires’ disease and Pontiac fever. For this reason, the growth and spread of Legionella bacteria must be limited as much as possible. This is done by controlling and monitoring various parameters in the water systems such as temperature, acidity and the presence of nutrients and other microorganisms. Nevertheless, it is always possible that there are still some of the Legionella bacteria present in the water systems. Therefore these water samples are examined by accredited laboratories.

OBJECTIVES: The aim of this study is to optimize the workflow of the detection and confirmation of Legionella colonies so that it becomes less a financially burdensome for the lab. This involves a comparative test between an immunochromatographic method of the VIRAPID® Legionella Culture test kit from Vircell and a mass spectrometric method with MALDI-TOF MS.

METHODS: In this comparative study, the lab procedure is temporarily adjusted. The inoculation and viewing of the plates continues to be performed in the same manner. Only the detection and confirmation of suspected colonies is performed differently. Thirty colonies are primarily confirmed with the test kit from Vircell. Subsequently, those same colonies are then also identified and confirmed by an analysis with MALDI-TOF MS. The comparison of the results of the two methods examines the extent to which they correspond to each other. Based on these results, the lab can consider adjusting the current workflow if this offers more financial benefits

RESULTS: The results of this study are divided into Legionella pneumophila and non-pneumohila speceis. Looking at the whole however, it can be seen that 83 % of the colonies are correctly identified after the first run on the MALDI-TOF MS. The colonies that gave a poor confidence score were analysed again. After the second run, this, the percentage of correct identification increases to 90 %.

CONCLUSION: The results of both methods are largely in agreement (90 %), but in 10 % of the cases it cannot be said with certainty that the results are analogous to each other. This, however, is only the beginning of the research and several more tests will have to be done before a concrete decision can be made about changing the workflow.


Ambachtsweg 3
9820 Merelbeke


Alexander De Meyer
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